Which setting on a profile makes a tab not accessible on the All Tabs page or visible in any app, but still allows a user Multiple Books to view records that would normally be found under this tab?

App Permissions manage access to application-level features and functionalities, not the visibility of individual tabs themselves.

Object Permissions determine a user's Create, Read, Update, Delete access to records for a specific object, but they do not control the visibility of the object's tab.

The 'Tab Settings' on a profile control the visibility of tabs within the Salesforce user interface. Setting a tab to 'Tab Hidden' ensures that the tab does not appear in any app or the All Tabs page, while still allowing users to access the underlying object's records if they have the necessary object permissions (e.g., through reports, search, or related lists).

Org-wide Defaults set the baseline sharing level for records across the organization, influencing data access, but have no direct impact on tab visibility.